Friction dampers generally apply a frictional force to a moveable member to dissipate translational or rotational energy of the member to produce acceptable member movement.
Prior art frictional dampers are typically comprised of surface effect dampers of the type described in U.S. Pat. No. 5,257,680 to Corcoran et al., and U.S. Pat. No. 4,957,279 to Thorn. Surface effect dampers operate by dissipating translational or rotational energy by working an elastomeric element to convert kinetic energy to heat. Such conventional dampers are generally comprised of a housing with an inner wall, and an elastomeric member movable through the housing. Interference between the inner wall and the elastomeric member produces the friction damping.
Additionally, frictional damping may be supplied to a movable member by a friction damper that utilizes a controllable fluid to precisely control the supplied damping force. Such devices are well known in the art as magnetorheological (MR) fluid devices and examples of MR devices can be found in commonly assigned U.S. Pat. No. 5,284,330 to Carlson et al.; and U.S. Pat. No. 5,277,281 also to Carlson et al. MR devices may be of the rotary or linear acting variety and such dampers employ a controllable MR fluid comprised of fine soft-magnetic particles disbursed within a liquid carrier. MR fluids exhibit a “thickening” behavior (a rheology change) sometimes referred to as an apparent viscosity change upon being exposed to a magnetic field of sufficient strength. The higher the magnetic field strength exposed to the MR fluid, the higher the damping force that can be achieved with a particular MR device. Although effective in providing damping in a large number of applications, conventional surface effect and MR friction dampers have a number of shortcomings. First, prior art dampers are sensitive to temperature changes and thermal expansion. When the prior art dampers are subjected to significant temperature increases or decreases the viscosity of the MR fluid may be affected and the change in fluid viscosity may in turn affect the supplied damping force. Such temperature changes can also affect the properties of the elastomer damping element and can cause the elastomeric damping element to contract or expand and experience dimensional changes. Changes to the damping element dimensions or properties will change the damping forces supplied by the surface effect friction damper.
Surface effect damping is provided by a carefully calculated interference, between the housing and elastomer element. In MR devices effective damping is ensured by maintaining a precisely defined gap dimension between the housing and piston member. The MR fluid flows through the defined gap. As a result of the foregoing, prior art dampers are very sensitive to dimensional tolerancing and tolerances must be tightly maintained in order for prior art friction dampers to provide effective damping forces. However, overtime, through repetitive use of the dampers, the critical tolerances between moving damper components are frequently lost and the deviations in the part tolerances negatively affects the forces provided by the friction damper. Finally, prior art friction dampers can be difficult to assemble and only a specific range of materials are acceptable for use in such prior art friction dampers.
The foregoing illustrates limitations known to exist in present devices and methods. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative friction damper is provided including features more fully disclosed hereinafter.